The present invention relates to a method of manufacturing semiconductor devices and a semiconductor manufacturing apparatus. More particularly, the invention relates to a manufacturing method of semiconductor devices and a semiconductor manufacturing apparatus which reduce the effect of particles (foreign matter particles) produced upon processing when manufacturing semiconductor devices by applying a plurality of steps of processing by means of plasma.
When manufacturing semiconductor devices typically represented by an LSI (large-scale integrated circuit) such as a microprocessor or a memory, it is necessary to conduct a plurality of processing steps including a step of forming thin films comprising various insulating films and a conductive film on a semiconductor substrate and a step of processing the thus formed thin films or the semiconductor substrate itself. When performing these processing steps, it is the present practice to use a plurality of semiconductor manufacturing apparatuses including a plasma etcher, a plasma CVD (chemical vapor deposition) apparatus and a plasma sputtering apparatus using the plasma technology.
In the step of processing a thin film formed on the semiconductor substrate into a desired shape, for example, the semiconductor substrate is transferred into a process chamber of a plasma etcher in such a state that a necessary area of the thin film is masked by a resist film for conducting plasma etching. A lower electrode which mounts the semiconductor substrate and an upper electrode arranged oppositely thereto are provided in the process chamber, and an etching gas is introduced into the process chamber. The etching gas is converted into plasma through generation of discharge in the process chamber by impressing a radio-frequency voltage onto the lower electrode to etch the portion not masked by a resist.
As is clear from FIG. 1, impression of radio-frequency power having a power P1 is started at time t1. After keeping power P1 for a certain period of time, impression of radio-frequency power is discontinued at time t2. The extent of generation of plasma is governed substantially by the radio-frequency power. In order to actually generate plasma, other conditions such as the amount of introduced plasma generating gas, the inner pressure in the process chamber and the like may also be taken into account.
When plasma-etching the thin film by use of the plasma etcher as described above, reaction products and the like are deposited in the process chamber. These deposits peel off, and adhere to the semiconductor substrate as particles, thereby contaminating the substrate. These stripped particles are produced similarly when applying processing by use of any of various plasma generators. For example, particles are produced as upon etching also when applying a plasma CVD processing by transferring the semiconductor substrate into the plasma CVD apparatus or when applying plasma sputtering by transferring the semiconductor substrate into a plasma sputtering apparatus. In these processing steps, each time the semiconductor. substrate is transferred to each plasma generator, processing the details of which are shown in FIG. 1 is repeated. This causes a further increase in the number of produced particles. Therefore, when manufacturing semiconductor devices through repetition of various steps of processing yield decreases under the effect of particles.
When manufacturing semiconductor devices through a plurality of processing steps by use of plasma, therefore, it is conventionally conceived to accomplish manufacture through a plurality of successive steps while holding semiconductor substrates in process chambers of a common plasma generator, by switching over the extent of radio-frequency power from time to time in response to the individual processing steps.
As illustrated in FIG. 2, in such a manufacturing method of semiconductor devices, a plurality of processes are carried out through a plurality of successive steps of conducting a process A by impressing a radio-frequency power of a power P1 onto the lower electrode during the period from time t1 to time t2; conducting a process B by impressing a radio-frequency power of a power P3 during the period from time t3 to time t4; conducting a process C by impressing a radio-frequency power of a power P2 during the period from time t5 to time t6; and conducting a process D by impressing a radio-frequency power of a power P4 during the period from time t7 to time t8.
In the existing manufacturing method of semiconductor devices, when conducting the method through a plurality of processes by means of plasma in a plurality of successive steps, a radio-frequency power is repeatedly started up and impressed for each step. This poses a problem of difficulty to reduce the effect of particles.
More specifically, in the existing manufacturing method of semiconductor devices, when conducting the plurality of processes through a plurality of successive steps, the radio-frequency power is repeatedly turned on and off for each of the steps. This results in stoppage of discharging each time. Because particles stripped off from the component parts of the process chamber are positively charged, the particles are confined in a sheath near the upper electrode or near the process chamber during plasma discharge. Upon stoppage of discharge and disappearance of plasma, the particles are attracted by the substrate having a negative self-bias potential, and adhere thereto. The particles dropping on the substrate during an interval between two steps may form defects through the next step.
Repetition of a steep change in radio-frequency power from 0 to a high power or from a high power to 0 for every step causes application of stress onto the film of reaction products adhering in the process chamber, and breakage and stripping of this film causes easier production of particles. Particularly, particles produced in the proximity of the semiconductor substrate are attracted by the negative self-bias potential of the semiconductor substrate even during discharge, and adhere thereto. The particles adhered to the semiconductor substrate in the middle of a step may form defects during the current or next step processing.